Before we can understand the present state of the psychology of religion – with its frequent emphasis on empirical data – it can be helpful to understand the field’s history. The prominent theoreticians that we explore in this chapter – James, Freud, Jung, Maslow, Fromm, Allport, Becker, Frankl, and others – remain influential in the twenty-first century, but they are also controversial. William James’ biography and writings show that debates about religion were never purely intellectual matters for the great scientist and philosopher. Freud’s theorizing on religion is discussed in detail, including his ideas on the origin and meaning of mystical religious experiences, the roots of theistic belief in wish-fulfillment, the notion of religion as a universal obsessional neurosis, and the assessment of the historical importance of religion for civilization. This discussion of Freud is followed by consideration of Carl Jung’s more sympathetic outlook on aspects of religion. The chapter concludes with a comprehensive discussion of the many ways humanistic and existential thinkers have studied religion and spirituality.

This chapter argues that throughout history many religions have proved themselves capable of sparking and fueling hostility toward outsiders and even toward people in the same faith who are viewed as unacceptable for one reason or another. We examine recent manifestations of extremism in Christianity, Hinduism, Buddhism, Judaism, and Islam, explaining that analysts often disagree about the extent to which religious beliefs and institutions are causally important. Key terms such as religious extremism, fundamentalism, radicalization, and terrorism are defined, noting the crucial importance of maintaining a distinction between the religious extremist and the extremely religious. Though we suggest researchers face many methodological challenges, we explore a broad range of empirical studies on related topics. The chapter also reviews theory and research on why and how people become religious extremists. We further draw on the psychology of radicalization, arguing that nowadays most scholars believe that there are cognitive and behavioral processes at work. Some people may move directly to carrying out terrorist deeds without acquiring much group ideology or religious belief.

Behaviorists, social learning theorists, evolutionary psychologists, cognitive psychologists, and neuroscientists have all brought their theories and methods to the study of human religious experience. This chapter explores how these approaches have added texture, depth, and data to the psychology of religion. We see that while most traditional behaviorists thought religious behavior did not require special theorizing, some psychologists of religion have relied heavily on classical conditioning, reinforcement contingencies, shaping, modeling, and other concepts from learning theory to explain religious life. Social cognitive theory has also been influential. In recent decades, an approach called the cognitive science of religion has built on work in evolutionary theory and cognitive psychology. This approach suggests that successful religious beliefs and practices have thrived precisely because they fit well with existing cognitive architecture – even though that architecture originally emerged for evolutionary reasons entirely unrelated to religion. The chapter concludes with an assessment of several approaches to religion grounded in biology and neuroscience.

The applied psychology of religion takes information from the knowledge base developed by psychologists of religion and uses this information for some social, psychological, or spiritual/religious purpose. When we seek to apply research and theory in this field we must first answer questions about our objectives, and it is unlikely that we will arrive at much agreement on ultimate goals. Still, it is possible that some consensual objectives and applications can emerge among researchers and those who seek to apply what researchers have learned. This chapter lists and discusses a broad range of potential applications. One major domain of application concerns clinical psychology, counseling psychology, psychiatry, social work, and related fields. We see that in recent decades, there have been many proposals – partly driven by the findings of empirical research – to integrate religious and spiritual approaches into mainstream psychotherapy. As with nearly everything else in the psychology of religion, these proposals can be controversial. In addition, the chapter discusses proposed spiritual and religious competencies for psychologists.

Survey data, despite limitations, offer the clearest window on the current state of global religiosity, showing the sharply divergent ways religious impulses and their absence have manifested in different nations and regions. After a discussion of religious literacy, we explore what cross-cultural survey research teaches about the global distribution of religious belief. Research suggests that atheism is rare, especially outside of Europe and a few industrialized countries. Beyond this, studies confirm that countries differ greatly in the prevalence of various religious beliefs, including belief in a personal God who intervenes in human affairs. Some careful projections also suggest that significant changes are coming over the next few decades in the relative sizes of different religious groups around the world. In the United States, survey data suggest that – despite some recent changes -- people continue to be relatively religious when compared with other highly industrialized and economically developed nations. The second half of the chapter looks at the empirical relationships between religiosity and education, intellect, thinking styles, gender, age, and personality.

Although people may – as some psychologists argue -- be born with a tendency to become believers, specific religious traditions are cultural products that must be acquired through learning and socialization. In addition, religious beliefs and behaviors take on different meanings at different ages. This chapter starts with a discussion of religious socialization and the developmental psychology of religion. The chapter includes a detailed section on religious socialization in summer camps. Next, we examine the large body of research on the psychology of prayer. Psychologists of religion argue that even if prayer involves some matters beyond the reach of science, important aspects of the prayer experience can be addressed using good scientific practice. T. M. Luhrmann’s important work is considered in some detail; she argues that, ultimately, through prayer, religious believers start to experience part of their own minds as the presence of God. The chapter concludes with two comprehensive sections on: (1) religious and mystical experiences and (2) identity and religion. For some people, religious identity is closely tied to ethnic, racial, national, professional, and familial identities; indeed, religious identity may be derived from these other identities.

In recent decades, scientific efforts to probe religious behavior and mental states have increased markedly in quantity and sophistication, yet the fascinating story of the psychology of religion remains unfamiliar not only to the general public, but also to many social scientists. This chapter starts with case studies of how religion has functioned in several prominent human lives. We consider why the psychology of religion matters and delve deeply into the many problems associated with defining religion, spirituality and the psychology of religion. The psychology of religion probes religious beliefs, attitudes, behaviors, emotions, experiences, and relationships, paying particular attention to the consequences of religion for health, well-being, morality and social relations. Scholars debate: (1) the importance of the field’s history and grand theories, (2) the acceptability of the historical emphasis on Western Christianity, (3) the generalizability of much empirical work, (4) the meaning of spirituality outside of religion, and (5) whether the discipline is biased in favor of or against religion.

Whatever their private religious convictions, nearly all contemporary psychologists of religion – when they act in professional roles – agree to operate in accordance with scientific rules. Recognition of the imperfections of individual methodologies has led to an emphasis on testing theories and verifying “facts” in multiple studies. Most of this chapter explores the pros and cons associated with various research methods, including experimentation, observation, and survey research. Although the logic of experimentation is undeniable and psychologists in various subfields frequently deem it the method of choice, many questions that we most want to answer in the psychology of religion cannot be addressed through experiments that are feasible, ethical, and convincing. Thus, the psychology of religion has always relied heavily on quantitative and qualitative survey research studies. Good surveys must strive to avoid biases rooted in question wording, question order, mode of data collection, social desirability, attitude-behavior discrepancies, and the tendency to overreport religious behavior. Fortunately, many existing measures of religious attitudes and behaviors have good psychometric qualities.